中点変位法によるランダム地形生成器

random_mapper.rb

#!ruby
require 'zlib'

PNG = 'sample.png'
WIDTH = 192
HEIGHT = 192

# 中点変位法による基礎データ生成
d = [WIDTH, HEIGHT].max
m = 1
m *= 2 while m < d
d = m
map = [[]]
map[0][0] = rand(256)
map[0][d] = rand(256)
map[d] = []
map[d][0] = rand(256)
map[d][d] = rand(256)
offx = 0
offy = 0
while d > 0
  0.step(m - 1, d) do |offy|
    0.step(m - 1, d) do |offx|
      map[offy + d / 2] = [] unless map[offy + d / 2]
      map[offy + d / 2][offx + d / 2] = ((map[offy][offx] + map[offy][offx + d] + map[offy + d][offx] + map[offy + d][offx + d]) / 4.0 + ((rand(d) - d / 2) * d / m)).to_i

      if offy <= 0
        map[offy][offx + d / 2] = ((map[offy][offx] + map[offy][offx + d] + map[offy + d / 2][offx + d / 2]) / 3.0 + ((rand(d) - d / 2) * d / m)).to_i
      else
        map[offy][offx + d / 2] = ((map[offy][offx] + map[offy][offx + d] + map[offy + d / 2][offx + d / 2] + map[offy - d / 2][offx + d / 2]) / 4.0 + ((rand(d) - d / 2) * d / m)).to_i
      end

      if offx <= 0
        map[offy + d / 2][offx] = ((map[offy][offx] + map[offy + d][offx] + map[offy + d / 2][offx + d / 2]) / 3.0 + ((rand(d) - d / 2) * d / m)).to_i
      else
        map[offy + d / 2][offx] = ((map[offy][offx] + map[offy + d][offx] + map[offy + d / 2][offx + d / 2] + map[offy + d / 2][offx - d / 2]) / 4.0 + ((rand(d) - d / 2) * d / m)).to_i
      end

      map[offy + d / 2][offx + d] = ((map[offy][offx + d] + map[offy + d][offx + d] + map[offy + d / 2][offx + d / 2]) / 3.0 + ((rand(d) - d / 2) * d / m)).to_i

      map[offy + d][offx + d / 2] = ((map[offy + d][offx] + map[offy + d][offx + d] + map[offy + d / 2][offx + d / 2]) / 3.0 + ((rand(d) - d / 2) * d / m)).to_i
    end
  end
  d /= 2
end

# いらん範囲は捨てる
map = map[0, HEIGHT].map{|e| e[0, WIDTH]}

# 各ピクセルの最大値・最小値を取って、0～255に正規化する
max, min = 0, 255
HEIGHT.times do |y|
  WIDTH.times do |x|
    max = [map[y][x], max].max
    min = [map[y][x], min].min
  end
end
diff = max - min
if diff < 255
  rate = 255.0 / diff
  HEIGHT.times do |y|
    WIDTH.times do |x|
      map[y][x] = ((map[y][x] - min) * rate).to_i
    end
  end
end

# パレット生成(てきとー)
col = []
col[0] = [0, 0, 0x10]
col[64] = [0x40, 0x40, 0xff]
col[72] = [0xc0, 0xc0, 0xc0]
col[80] = [0x60, 0xc0, 0x60]
col[128] = [0x40, 0xc0, 0x40]
col[192] = [0x20, 0x90, 0x20]
col[208] = [0x80, 0x60, 0x60]
col[224] = [0x90, 0x80, 0x80]
col[255] = [0xff, 0xff, 0xff]
col.size.times do |n|
  unless col[n]
    x = n - 1
    while true
      prev = col[x]
      break if col[x]
      x -= 1
    end
    y = n + 1
    while true
      break if col[y]
      y += 1
    end
    col[n] = []
    col[n][0] = (col[x][0] + (col[y][0] - col[x][0]) * 1.0 / (y - x)).to_i
    col[n][1] = (col[x][1] + (col[y][1] - col[x][1]) * 1.0 / (y - x)).to_i
    col[n][2] = (col[x][2] + (col[y][2] - col[x][2]) * 1.0 / (y - x)).to_i
  end
end

# PNG出力
# やってることの中身はmameさんの日記を参照
# http://d.hatena.ne.jp/ku-ma-me/20091003/
def chunk(hdr, data)
  [data.bytesize, hdr, data, Zlib.crc32(hdr + data)].pack('NA4A*N')
end

open(PNG, 'wb') do |f|
  f.print "\x89PNG\r\n\x1a\n"
  f.print chunk('IHDR', [WIDTH, HEIGHT, 8, 2, 0, 0, 0].pack('NNCCCCC'))
  data = ''
  HEIGHT.times do |y|
    data << [0, *map[y].map{|e| col[e]}.flatten].pack('C*')
  end
  f.print chunk('IDAT', Zlib.deflate(data, 9))
  f.print chunk('IEND', '')
end